Radio clock, radio wave receiver, and radio wave receiving method

ABSTRACT

A radio wave receiver, that receives satellite waves, includes a GPS reception processing unit configured to receive signals from a plurality of positioning satellites, acquire data necessary for positioning from the received signals, calculate a current location of the radio wave receiver, save a failure history related to acquisition of the data necessary for positioning with respect to each of the received signals, determine a reception condition of each of the received signals in accordance with the failure history, and suspend acquisition of the data necessary for positioning with respect to a signal having the reception condition determined to be at least equal to a predetermined reference level, the signal being among the signals from the plurality of positioning satellites.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a Divisional of U.S. application Ser. No. 14/830,498 filed Aug.19, 2015, which is based upon and claims the benefit of priority fromprior Japanese Patent Application No. 2014-181024, filed Sep. 5, 2014,the entire contents of both of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

The present invention relates to a radio controlled timepiece thatacquires information by receiving radio waves from positioningsatellites.

There have been electronic clocks (radio controlled timepieces) thatreceive radio waves containing date and time information and locationinformation, and perform date and time correction, time zone setting,and the like. Performing such operations in accordance with movement ofa user, a lapse of a predetermined time, and the like, a radiocontrolled timepiece readily and accurately counts the date and time,and can display the local time in accordance with the current locationof the user.

There are positioning satellites according to GNSS (Global NavigationSatellite System) as one type of information source that radio-transmitsdate and time information and location information from outside byradio. Radio waves from positioning satellites can be received anywherein the world as long as the sky is visible. Accordingly, there are onlya few restrictions on such radio waves, and such radio waves arepreferably used in portable radio controlled timepieces.

Meanwhile, to receive radio waves from positioning satellites, a muchlarger load is normally required, compared with the electrical loadnecessary in a counting operation or a display operation to be performedin an electronic clock. In a portable radio controlled timepiece, orparticularly a wristwatch, a power supply that readily copes with alarge load cannot be used, as the small size and the light weight needto be maintained. In view of this, technologies have been developed forreducing power consumption by shortening the time required to receiveradio waves from a positioning satellite in various manners.

However, if an upper limit is set on reception periods, the possibilitythat information can be successfully acquired becomes lower. In view ofthis, JP 2010-60456 A discloses a technology by which thereception-restricted time is varied depending on the intensity ofreception from a positioning satellite, and any extension of thereception-restricted time is not allowed when the remaining batterylevel is low.

Even when the reception level is high, information is not necessarilyacquired successfully in a short time, due to temporary noise or thelike. When the reception level is low, on the other hand, even ifinformation is successfully acquired, its precision might be too low andcause a problem in practical use. In such cases, there are only lowpossibilities that information can be successfully acquired in spite oflong reception periods, and failed information acquisition is likely toconsume electric power for nothing.

The present invention relates to a radio controlled timepiece that canefficiently acquire information from positioning satellites.

SUMMARY OF THE INVENTION

To achieve the above object, the present invention provides a radiocontrolled timepiece that receives radio waves transmitted from apositioning satellite, and includes

a GPS reception processing unit configured to

search for and capture a signal from a positioning satellite, the signalbeing included in received radio waves,

demodulate and decode the captured signal, to acquire the datacorresponding to acquisition target information in data transmitted fromthe positioning satellite,

acquire the acquisition target information, using the acquired data,

hold a failure history related to acquisition of the data with respectto each captured signal,

suspend acquisition of the data from a signal having a reception leveldetermined to be at least equal to a predetermined reference level basedon the failure history, and

end acquisition of the data when the number of signals from which thedata is to be acquired after search for the signal is ended under apredetermined condition becomes smaller than the number of signalsnecessary in acquiring the acquisition target information.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the functional structure of anelectronic clock according to an embodiment of the present invention;

FIG. 2A is a block diagram showing the internal structure of a GPSreception processing unit;

FIG. 2B is a block diagram showing the internal structure of a controlunit of the GPS reception processing unit;

FIG. 3 is a flowchart showing the control procedures in a local timeacquisition process to be performed by the GPS reception processing unitof an electronic clock according to a first embodiment;

FIG. 4 is a flowchart showing the control procedures in a local timeacquisition process according to a first modification;

FIG. 5 is a flowchart showing the control procedures in a local timeacquisition process according to a second modification;

FIG. 6 is a block diagram showing the functional structure of anelectronic clock according to a second embodiment; and

FIG. 7 is a flowchart showing the control procedures in a local timeacquisition process to be performed by the GPS reception processing unitof the electronic clock according to the second embodiment.

DETAILED DESCRIPTION

The following is a description of embodiments of the present invention,with reference to the accompanying drawings.

FIG. 1 is a block diagram showing the functional structure of anelectronic clock 1 according to an embodiment of the present invention.

This electronic clock 1 is a radio controlled timepiece that can be usedwhen receiving radio waves from positioning satellites.

The electronic clock 1 according to a first embodiment includes a CPU 41(Central Processing Unit) (the clock control unit), a ROM 42 (Read OnlyMemory), a RAM 43 (Random Access Memory), an oscillator circuit 44, adivider circuit 45, a timer circuit 46, an operating unit 47, a standardwave receiving unit 48 and its antenna 49, a GPS reception processingunit 50 and its antenna 51, a drive circuit 52, a power supply unit 53,a second hand 61, a minute hand 62, an hour hand 63, a date wheel 64, afunction index 65, train wheel mechanisms 71 through 74, and steppingmotors 81 through 84. Hereinafter, some or all of the second hand 61,the minute hand 62, the hour hand 63, the date wheel 64, and thefunction index 65 will also be collectively referred to as indexes 61through 65.

The CPU 41 performs various kinds of arithmetic processing, and controlsentire operation of the electronic clock 1 in an integrated manner. TheCPU 41 controls index operation related to display of a date and time,and calculates the date and time by operating the standard wavereceiving unit 48 and acquiring received data. Based on the acquireddate and time data, the CPU 41 corrects the date and time counted by thetimer circuit 46.

The ROM 42 stores a program 421 for various kinds of control to beperformed by the CPU 41, and setting data. The program 421 includes aprogram related to operation control in various functional modes, forexample.

The RAM 43 provides the CPU 41 with a work memory space, and storestemporary data.

The oscillator circuit 44 generates and outputs a predeterminedfrequency signal. The oscillator circuit 44 includes a crystaloscillator, for example.

The divider circuit 45 divides the frequency signal output from theoscillator circuit 44 into signals at frequencies to be used by the CPU41 and the timer circuit 46, and outputs the signals. The frequencies tobe output may be changeable in accordance with a control signal from theCPU 41.

The timer circuit 46 counts the current date and time by adding adivided signal input from the divider circuit 45 to an initial valueindicating a predetermined date and time. The date and time counted bythe timer circuit 46 can be corrected in accordance with a controlsignal from the CPU 41.

The operating unit 47 accepts an input operation from a user. Theoperating unit 47 includes push-button switches and a rotary switch.When one of the push-button switches is pressed or released, or when therotary switch is pulled out and rotated or is pushed back, an electricalsignal indicating the corresponding operation is output as an interruptsignal to the CPU 41.

The standard wave receiving unit 48 receives radio waves (standardwaves) in a long-wavelength band using the antenna 49, demodulates theamplitude-modulated time signal output (TCO) of the standard waves, andoutputs the time signal to the CPU 41. The tuning frequency in thelong-wavelength band according to the standard wave receiving unit 48 ischanged depending on a transmission frequency from a station thattransmits the standard waves to be received under the control of the CPU41. The standard wave receiving unit 48 also performs various kinds ofprocessing for increasing receiving sensitivity, digitizes an analogsignal at a predetermined sampling frequency, and outputs the digitizedsignal to the CPU 41.

Using the antenna 51, the GPS reception processing unit 50 receivesradio waves in the L1 band (1.57542 GHz) being transmitted from apositioning satellite, and demodulates and decodes a signal (navigationmessage) from the positioning satellite, to acquire date and timeinformation and location information. The acquired information isoutput, to the CPU 41, in a format that is set in accordance with theNMEA (National Marine Electronics Associations)-0182 standards or thelike. The GPS reception processing unit 50 receives, from the CPU 41,the information to be acquired and the settings related to the outputformat, and stores the information and the settings. The GPS receptionprocessing unit 50 also stores predicted orbit information that isacquired from a positioning satellite and is about the positioningsatellite, and can read and use the predicted orbit information asnecessary at a time of reception. A time-zone correspondence table 502 dfor acquiring the time zone corresponding to a designated location ordaylight-saving-time information is also stored in the GPS receptionprocessing unit 50.

The drive circuit 52 receives a control signal from the CPU 41, outputsa drive signal to the corresponding one of the stepping motors 81through 84 at an appropriate time in accordance with the control signal,and rotatively drives the corresponding one of the stepping motors 81through 84. Based on the settings input from the CPU 41, the drivecircuit 52 can adjust the pulse width of the drive signal and the drivevoltage as appropriate. In a case where a control signal forsimultaneously driving more than one stepping motor so as not to apply ahigh load at once is input, the drive circuit 52 can rotatively drivethose stepping motors sequentially at very short intervals so that thestepping motors are not driven in an overlapping manner.

The power supply unit 53 supplies the power for operations of therespective components at a predetermined voltage. The power supply unit53 includes a battery, and this battery may be an exchangeablebutton-type dry-cell battery, for example. Alternatively, a solar paneland a secondary cell may be used as the battery. In a case wheredifferent voltages are output from the power supply unit 53, thevoltages can be converted into a desired voltage by a switching powersupply, for example, and be then output.

The stepping motor 81 rotatively moves the second hand 61 via the trainwheel mechanism 71 that is an array of gear wheels. When the steppingmotor 81 is driven once, the second hand 61 rotates six degrees in onestep. While the stepping motor 81 is driven 60 times, the second hand 61comes full circle on the clock face.

The stepping motor 82 rotatively moves the minute hand 62 and the hourhand 63 via the train wheel mechanism 72. The train wheel mechanism 72is designed to rotate the hour hand 63 in conjunction with the minutehand 62, and rotates the hour hand 63 one-twelfth of a degree whilerotating the minute hand 62 one degree.

The stepping motor 83 rotatively moves the date wheel 64 via the trainwheel mechanism 73. The date wheel 64 is provided at a lower portion ofthe clock face for displaying the indexes (or on the back side) of theelectronic clock 1, and can rotate parallel to the clock face fordisplaying the indexes, though not particularly limited. While anopening is formed in the clock face, respective indicators that indicatethe first through 31st days are provided on the circumference of thedate wheel 64 facing the opening, and one of the indicators is exposedthrough the opening as the date wheel 64 rotatively moves. When thestepping motor 83 is driven once, the date wheel 64 rotatively moves thedegrees equivalent to one step. While the stepping motor 83 rotativelymoves 150 steps, the date wheel 64 rotatively moves 360/31 degrees, sothat the date indicator exposed through the opening of the clock facechanges by one day. When the date wheel 64 completes rotating by theamount equivalent to 31 days, the date indicator indicating the firstday is again exposed through the opening.

The stepping motor 84 rotatively moves the function index 65 via thetrain wheel mechanism 74. The function index 65 rotates about adifferent rotation axis from any of the second hand 61, the minute hand62, the hour hand 63, and the date wheel 64, for example, and is usedfor displaying contents other than date display or displaying the typeof the contents. The train wheel mechanism 74 rotates the function index65 six degrees, as the stepping motor 84 revolves once, for example.

Next, radio wave reception by the GPS reception processing unit 50 frompositioning satellites is described.

FIG. 2A is a block diagram showing the internal structure of the GPSreception processing unit 50.

FIG. 2B is a block diagram showing the internal structure of a controlunit 502 c of the GPS reception processing unit 50.

The GPS reception processing unit 50 includes an RF (Radio Frequency)unit 501 connected to the antenna 51, and a baseband unit 502 connectedto the RF unit 501.

The RF unit 501 amplifies a signal from radio waves received by theantenna 51, and converts the signal into a signal frequency (abaseband). The RF unit 501 includes a LNA (Low Noise Amplifier), a BPF(Band Pass Filter), a local oscillator, a mixer, and an IF (IntermediateFrequency) amplifier, for example, and converts signals into a basebandsignal around an intermediate frequency by a superheterodyne system.

The baseband unit 502 searches the signals converted into the basebandsignal for signals from respective positioning satellites, and capturesthe signals. The baseband unit 502 then demodulates and decodes thecaptured signals, to acquire desired information. The baseband unit 502includes a capturing unit 502 a, a tracking unit 502 b, and the controlunit 502 c (an information acquiring unit 502 c 1, a reception controlunit 502 c 2, and a determining unit 502 c 3). The capturing unit 502 ainversely spreads a spectrum by sequentially applying respectivepseudonoise signals (C/A codes) set for the positioning satellites to becaptured to the baseband signal, and calculates correlation values. Bydoing so, the capturing unit 502 a searches for and captures signalsfrom the positioning satellites related to the C/A codes. The trackingunit 502 b demodulates and decodes a navigation messages of thepositioning satellites by sequentially using the C/A codes of thepositioning satellites captured by the capturing unit 502 a inidentified phases, and acquires the necessary data for acquiring thecurrent location (the information to be acquired), or information aboutthe date and time contained in sub-frames 1 through 3 (includingcorrection information) and predicted orbit information (an ephemeris).

The control unit 502 c controls operation of the baseband unit 502. Thecontrol unit 502 c includes a CPU (module CPU), a RAM, and a storageunit. The module CPU switches on and off operations of the capturingunit 502 a and the tracking unit 502 b, selects and controls thepositioning satellites to be received, and performs setting and controlrelated to data exchange with the CPU 41. The module CPU also calculates(acquires) the current location, using the date and time information andthe predicted orbit information acquired by the tracking unit 502 b. TheRAM is a volatile memory that provides the module CPU with a work memoryspace. The storage unit stores predicted orbit data (an ephemeris oralmanac) acquired from the positioning satellites, and the settingsrelated to the past reception history and the information to bereceived. The data and the settings are read and used as necessary. Thecapturing unit 502 a can cause search engines (capture processing units)for channels ch1 through chn (n being 16, for example) to search forsignals in parallel. The tracking unit 502 b can enable demodulation anddecoding of signals on channels ch1 through chm (m being 8, for example)in parallel. In a case where signals from 32 satellites are searched forin parallel, 16 satellites and the other 16 satellites are alternatelysearched.

The control unit 502 c can switch on and off operations of the capturingunit 502 a and tracking unit 502 b independently of each other. Thecontrol unit 502 c can also set the positioning satellites related tothe signals to be captured by the capturing unit 502 a. For example, thecontrol unit 502 c can exclude a positioning satellite that has alreadybeen captured by the capturing unit 502 a and is being tracked by thetracking unit 502 b, from the positioning satellites to be captured.

In accordance with a setting as to whether positioning satellitesaccording to GPS and GLONASS are used, or whether only positioningsatellites according to one of the positioning systems are used, thecontrol unit 502 c can expand the positioning satellites to be capturedto both systems or further to Galileo, or can limit the positioningsatellites to be captured to one of the systems.

In a case where predicted orbit information is held at a time oflocation measurement, or where predicted orbit information is acquiredduring reception, the control unit 502 c can exclude, from thepositioning satellites to be captured, the positioning satellitesrelated to signals that cannot be received at ground level at the sametime as already-captured signals, in accordance with the predicted orbitinformation. Further, in a case where general location information isstored in advance, signals from the positioning satellites located insuch positions that the signals cannot be received may be excluded fromthe signals to be captured, in accordance with the location informationand the current date and time.

Next, a location measuring operation in the electronic clock 1 isdescribed. Signals from positioning satellites are spectrum-spread withC/A codes unique to the respective positioning satellites, and areradio-transmitted. Therefore, the capturing unit 502 a calculatescorrelation values with respect to the respective C/A codes, andidentifies C/A codes having high correlation values and their phases, tocapture signals from the positioning satellites corresponding to the C/Acodes. The tracking unit 502 b demodulates and decodes the capturedsignals with the C/A codes used in the capture and in the phases. Thisprocess is continued.

In a case where signals from positioning satellites according to GPS(GPS satellites) are received, a signal to be demodulated is formed with25 repetitions (pages) of 30-second frame data formed with fivesix-second sub-frames. Of these sub-frames, the first sub-frame data(sub-frame 1) through third sub-frame data (sub-frame 3) of any desiredpage are acquired. In this manner, data related to the date and timeinformation and the satellite orbit information necessary for locationmeasurement are acquired. In three-dimensional location measurement, thesatellite orbit information (satellite locations) and the date and timeinformation (timing) about four satellites are necessary. In a casewhere there is no need to obtain information about the height direction,however, location measurement on the ground surface is assumed so thatlocation measurement can be carried out with the satellite orbitinformation and the date and time information about three satellites(three is the necessary number in acquiring the information to beobtained).

However, depending on the arrangement (coordinates) of the positioningsatellites to be used in location measurement (in a case where thepositioning satellites to be used in location measurement are aligned ona line, for example), locations might not be determined with highprecision in a three-dimensional space or in a two-dimensional plane onthe ground surface. As the parameter indicating the positioningprecision in accordance with such coordinates, DOP (Dilution ofPrecision, or P (Position) DOP in the case of four satellites, or H(Horizontal) DOP in the case of two-dimensional location measurementwith three satellites) is calculated. Allowable precision is set asappropriate in accordance with products and purposes of use.

In the electronic clock 1 of this embodiment, the GPS receptionprocessing unit 50 acquires the data of the sub-frames 1 through 3 fromat least three positioning satellites, and carries out locationmeasurement. If the value of the DOP related to this locationmeasurement satisfies a predetermined condition (or is equal to orsmaller than a predetermined reference value), the result of thelocation measurement is determined to be an accurate result.

FIG. 3 is a flowchart showing the control procedures to be carried outby the control unit 502 c in a local time acquisition process to beperformed by the GPS reception processing unit 50 of the electronicclock 1 of this embodiment.

This local time acquisition process is started when a predeterminedinput operation performed on the operating unit 47 by a user isdetected, for example. Alternatively, the local time acquisition processmay be started when a predetermined operation condition is satisfied.

When the local time acquisition process is started, the control unit 502c (module CPU) activates the RF unit 501 and the capturing unit 502 a,and causes the RF unit 501 and the capturing unit 502 a to startoperations related to reception of radio waves in the L1 band andcapture of signals from positioning satellites (step S101). At thispoint, the control unit 502 c starts counting the elapsed time after thestart of capture (capture elapsed time).

The control unit 502 c determines whether the capture elapsed time hasexceeded a predetermined capture time-out period (upper limit period)(step S102). If the control unit 502 c determines that the captureelapsed time has not exceeded the capture time-out period (“NO” in stepS102), the control unit 502 c determines whether there is a newlycaptured signal from a positioning satellite (step S103). If the controlunit 502 c determines that there is a newly captured signal (“YES” instep S103), the control unit 502 c causes the tracking unit 502 b tostart an operation to demodulate and decode a navigation message relatedto the captured positioning satellite, and causes the capturing unit 502a to end the capture of the signal (step S104).

The control unit 502 c then determines whether the number of capturedsignals is equal to or larger than a predetermined number (step S106).This predetermined number is equal to or larger than the smallest numberof necessary satellites (three satellites) in location measurement, andis a value that is set by taking into account a case where acquisitionof a navigation message is unsuccessful after capture, or where a signalof a positioning satellite having undesirable coordinates is capturedfirst. This predetermined number is normally set between four and eight,or five, for example. If the control unit 502 c determines that thepredetermined number or more of signals have been captured (“YES” instep S106), the control unit 502 c causes the capturing unit 502 a toend the capturing operation, and stops the capturing unit 502 a (stepS121). At this point, the control unit 502 c starts counting thetracking elapsed time from the time when the capture is ended. If thecontrol unit 502 c determines that the predetermined number or more ofsignals have not been captured yet (“NO” in step S106), the processbeing performed by the control unit 502 c moves on to step S112.

The control unit 502 c then determines whether the tracking elapsed timehas exceeded a predetermined tracking time-out period (step S122). Ifthe control unit 502 c determines that the tracking elapsed time hasexceeded the tracking time-out period (“YES” in step S122), the processbeing performed by the control unit 502 c moves on to step S133, and thecontrol unit 502 c ends the receiving operation, and ends the local timeacquisition process. If the control unit 502 c determines that thetracking elapsed time has not exceeded the tracking time-out period(“NO” in step S122), the control unit 502 c determines whether the dataof the sub-frames 1 through 3 in navigation messages have been acquiredin the tracking unit 502 b from three or more positioning satellitesamong the captured positioning satellites (step S123).

If the control unit 502 c determines that the data of the sub-frames 1through 3 have not been acquired yet from three or more positioningsatellites (“NO” in step S123), the process being performed by thecontrol unit 502 c returns to step S122. If the control unit 502 cdetermines that the data of the sub-frames 1 through 3 have beenacquired (“YES” in step S123), the control unit 502 c determines whetherthe acquired result of location measurement satisfies a predeterminedprecision condition (step S127). The control unit 502 c determineswhether the value of the DOP is equal to or smaller than thepredetermined reference value. If the control unit 502 c determines thatthe value of the DOP is equal to or smaller than the reference value, orthat the precision of the result of location measurement is equal to orhigher than a predetermined precision (or satisfies a predeterminedcriterion) (“YES” in step S127), the control unit 502 c causes thetracking unit 502 b to end the tracking operation, and stops thetracking unit 502 b (step S128). The control unit 502 c refers to thetime-zone correspondence table 502 d, and identifies a time zone basedon acquired location information (step S129). At this point, the controlunit 502 c outputs the correct date and time, and time zone informationto the CPU 41 at an appropriate time, so that the date and time on thetimer circuit 46, and the local time to be displayed can be corrected.The control unit 502 c then ends the local time acquisition process.

If the control unit 502 c determines in the determination procedure instep S127 that the result of local measurement does not satisfy theprecision condition (“NO” in step S127), the control unit 502 cdetermines whether the data of the sub-frames 1 through 3 have beenacquired from all the captured positioning satellites (step S131). Ifthe control unit 502 c determines that the data of the sub-frames 1through 3 have not been acquired at all, or have not been acquired fromone or more captured positioning satellites (“NO” in step S131), theprocess being performed by the control unit 502 c moves on to step S122.If the control unit 502 c determines that the data of the sub-frames 1through 3 have been acquired from all the captured positioningsatellites (“YES” in step S131), the control unit 502 c ends thereception process related to all the positioning satellites (step S133),and ends the local time acquisition process.

If the control unit 502 c determines in the procedure in step S103 thatthere are no new signals acquired during the capturing operation beingperformed by the capturing unit 502 a (“NO” in step S103), the controlunit 502 c determines whether the number of currently capturedpositioning satellites (the number of captured positioning satellites)is “0” (step S111). If the control unit 502 c determines that the numberof captured positioning satellites is “0” (“YES” in step S111), theprocess being performed by the control unit 502 c moves on to step S102.If the control unit 502 c determines that the number of capturedpositioning satellites is not “0” (“NO” in step S111), the process beingperformed by the control unit 502 c moves on to step S112.

After the process moves from step S111 or step S106 to step S112, thecontrol unit 502 c determines whether the data of the sub-frames 1through 3 have been acquired from three or more positioning satellitesamong the positioning satellites acquired so far (step S112). If thecontrol unit 502 c determines that the data of the sub-frames 1 through3 have not been acquired, or that the number of captured positioningsatellites is smaller than three or the data of the sub-frames 1 through3 have not been acquired (“NO” in step S112), the process beingperformed by the control unit 502 c moves on to step S102.

If the control unit 502 c determines in the determination procedure instep S112 that the data of the sub-frames 1 through 3 have been acquiredfrom three or more positioning satellites (“YES” in step S112), theprocess being performed by the control unit 502 c returns to step S127.At this point, the control unit 502 c ends the capturing operation bythe capturing unit 502 a.

If the control unit 502 c determines in the determination procedure instep S102 that the capture elapsed time has exceeded the capturetime-out period without the number of captured positioning satellitesbecoming equal to or larger than the predetermined number (“YES” in stepS102), the control unit 502 c determines whether three or morepositioning satellites have been captured (step S109). If the controlunit 502 c determines that three or more positioning satellites havebeen captured (“YES” in step S109), the process being performed by thecontrol unit 502 c moves on to step S121. If the control unit 502 cdetermines that three or more positioning satellites have not beencaptured yet (or that only two or less positioning satellites have beencaptured) (“NO” in step S109), the process being performed by thecontrol unit 502 c moves on to step S133, ends the reception (thecapture and the tracking), and ends the local time acquisition process.

First Modification

Next, a first modification of the local time acquisition process in theelectronic clock 1 of this embodiment is described.

FIG. 4 is a flowchart showing the control procedures to be carried outby the control unit 502 c in a local time acquisition process accordingto the first modification.

In this local time acquisition process, the procedure in step S123 inthe local time acquisition process of the above described embodiment isdivided into steps S123 a and S123 b, the procedure in step S112 isdivided into steps S112 a and S112 b, and further, the procedures insteps S124 through S126 and steps S113 and S114 are added. Theprocedures other than these procedures are the same as those of theabove described embodiment, and are denoted by the same referencenumerals as those used in the above described embodiment. Therefore,detailed explanation of them is not provided herein.

If the control unit 502 c determines in the determination procedure instep S111 that the number of captured positioning satellites is not “0”(“NO” in step S111), the control unit 502 c determines whether it is thetime when the data of the sub-frames 1 through 3 have been acquired fromeach of the captured positioning satellites (step S112 a). That is,after a location in a navigation message is identified in each of thepositioning satellites (or after the process branches into “YES” in theprevious procedure in step S112 a), the control unit 502 c determineswhether all the reception periods for the sub-frames 1 through 3 havepassed. The sequence of the reception periods is not necessarily equalto the order of the sub-frames 1, 2, and 3, and the sub-frame 1 or 2 inthe next frame may be received after the sub-frame 3 is received, forexample. That is, depending on the signal capture timing (the time tostart acquiring data), the data of one frame (one cycle) may not startfrom the sub-frame 1.

If the control unit 502 c determines that it is the time when the dataof the sub-frames 1 through 3 have not been acquired from any of thecaptured satellites (“NO” in step S112 a), the process being performedby the control unit 502 c returns to step S102. If the control unit 502c determines that it is the time when all the data reception periods forthe sub-frames 1 through 3 have passed in one of the satellites (“YES”in step S112 a), the control unit 502 c adds “1” to the number of timesreception has been performed from the positioning satellite with whichacquisition of the data of the sub-frames 1 through 3 has beenunsuccessful among the positioning satellites that have reached the time(step S113) (the number of times reception has been performed isreferred to as the “failure history”, and the initial value of thenumber of times of reception is “0”). The control unit 502 c alsosuspends the tracking operation for each positioning satellite withwhich the number of times of reception is a predetermined number oftimes (a predetermined upper limit number of times), or two or larger(or the reception level becomes equal to or lower than a referencelevel) (step S114).

The control unit 502 c then determines whether the data of thesub-frames 1 through 3 have been acquired from signals related to threeor more positioning satellites (or whether the number is equal to orlarger than the necessary number for acquiring the information to beacquired) (step S112 b). If the control unit 502 c determines that thedata of the sub-frames 1 through 3 have been acquired from three or morepositioning satellites (“YES” in step S112 b), the process beingperformed by the control unit 502 c moves on to step S127. If thecontrol unit 502 c determines that the data of the sub-frames 1 through3 have not been acquired from three or more positioning satellites, orthat the number is smaller than the necessary number for locationmeasurement (“NO” in step S112 b), the process being performed by thecontrol unit 502 c returns to step S102.

If the control unit 502 c determines in the determination procedure instep S122 that the tracking elapsed time has not exceeded the trackingtime-out period (“NO” in step S122), the control unit 502 c determineswhether it is the time when the data of the sub-frames 1 through 3 havebeen acquired from each of the captured positioning satellites (stepS123 a). After a location in a navigation message is identified in asignal from each positioning satellite, the control unit 502 cdetermines whether all the reception periods for the sub-frames 1through 3 have passed.

If the control unit 502 c determines that it is the time when the dataof the sub-frames 1 through 3 have not been acquired from any of thecaptured satellites (“NO” in step S123 a), the process being performedby the control unit 502 c returns to step S122. If the control unit 502c determines that it is the time when the date of the sub-frames 1through 3 have been acquired from one of the satellites (“YES” in stepS123 a), the control unit 502 c adds “1” to the number of timesreception has been performed from the positioning satellite with whichacquisition of the data of the sub-frames 1 through 3 has beenunsuccessful among the positioning satellites that have reached the time(step S124) (the initial value of the number of times of reception is“0”). The control unit 502 c also suspends the tracking operation foreach positioning satellite with which the number of times of receptionis a predetermined number of times, or two or larger (step S125).

Later in the determination procedure in step S131, “all the capturedsatellites” do not include the positioning satellites for which thetracking operation has been suspended in the procedures in steps S114and S125 (or those positioning satellites are regarded as not havingbeen captured in the first place).

The control unit 502 c then determines whether the number of positioningsatellites being currently tracked is smaller than three (step S126). Ifthe control unit 502 c determines that the number of positioningsatellites being currently tracked is smaller than three (“YES” in stepS126), the process being performed by the control unit 502 c moves on tostep S133, and the control unit 502 c ends the receiving operation (stepS133), and ends the local time acquisition process.

If the control unit 502 c determines that the number of positioningsatellites being currently tracked is not smaller than three (is threeor larger) (“NO” in step S126), the control unit 502 c determineswhether the data of the sub-frames 1 through 3 have been acquired fromthree or more positioning satellites (step S123 b). If the control unit502 c determines that the data of the sub-frames 1 through 3 have beenacquired from three or more positioning satellites (“YES” in step S123b), the process being performed by the control unit 502 c moves on tostep S127. If the control unit 502 c determines that the data of thesub-frames 1 through 3 have not been acquired from three or morepositioning satellites (“NO” in step S123 b), the process beingperformed by the control unit 502 c returns to step S122.

Second Modification

FIG. 5 is a flowchart showing the control procedures to be carried outby the control unit 502 c in a second modification of the local timeacquisition process.

In the second modification of the local time acquisition process, theprocedures in steps S106 and 115 are further added to the local timeacquisition process of the above described first modification. Thedetails and procedures of the process other than these procedures arethe same as those of the first modification, and are denoted by the samereference numerals as those used in the first modification. Therefore,detailed explanation of them is not provided herein.

When the tracking unit 502 b is made to start an operation to track anewly captured signal in the procedure in step S104, the control unit502 c adjusts the number of search engines to be operated, in accordancewith the number of satellites to be captured that decreases as signalsrelated to the positioning satellites to be tracked are excluded fromthe signals to be captured by the capturing unit 502 a (step S105). Forexample, in a case where the capturing unit 502 a includes 16 searchengines and is to capture 32 GPS satellites, the capturing unit 502 aperforms a process of capturing signals of the 32 GPS satellites byalternately searching 16 GPS satellites and the other 16 GPS satellitesof the 32 GPS satellites. In a case where two GSP satellites arecaptured, the control unit 502 c can stop one of the search engines, andchange the setting so that the remaining 15 search engines alternatelysearch 15 GPS satellites and the other 15 GPS satellites for signals ofthe remaining 30 GPS satellites. The process being performed by thecontrol unit 502 c then moves on to step S106.

Also, after suspending the data acquisition from signals of apositioning satellite having a number of times of reception equal to orlarger than the predetermined number of times in the procedure in stepS114, the control unit 502 c excludes the positioning satellite from thepositioning satellites to be captured by the capturing unit 502 a (stepS115). That is, after acquisition of the data of the sub-frames 1through 3 is unsuccessful, and the tracking operation is suspended, thesignals of once-captured positioning satellites are not searched foragain. The process being performed by the control unit 502 c then moveson to step S112 b.

As described above, the electronic clock 1 of the first embodimentincludes: the capturing unit 502 a that searches for and capturessignals from positioning satellites included in radio waves; thetracking unit 502 b that demodulates and decodes the captured signals,and acquires the sub-frames 1 through 3 necessary for locationmeasurement among the data transmitted from the positioning satellites;and the control unit 502 c. The control unit 502 c acquires the currentlocation, using the data of the sub-frames 1 through 3 acquired by thetracking unit 502 b (the control unit 502 c serving as an informationacquiring unit). The control unit 502 c holds the failure historyrelated to acquisition of the data of the sub-frames 1 through 3 foreach signal, and causes the tracking unit 502 b to suspend theacquisition of the data of the sub-frames 1 through 3 from signals atreception levels equal to or lower than a predetermined reference levelbased on the failure history. In a case where the number of signals fromwhich the data of the sub-frames 1 through 3 are to be acquired becomessmaller than three due to the above mentioned suspension after thecapturing unit 502 a is made to end signal search under a predeterminedcondition, the control unit 502 c causes the GPS reception processingunit 50 to end the reception operation (the control unit 502 c servingas a reception control unit).

That is, if a tracking time-out period is simply set in an operation tobe performed by the tracking unit 502 b, the operation is continueduntil the tracking time-out period has passed, regardless of variationsin timing of capture. In this electronic clock 1, on the other hand,whether reception of the sub-frames 1 through 3 is difficult isdetermined with respect to each positioning satellite. Accordingly, itis possible to impartially determine whether the sub-frames 1 through 3can be sufficiently acquired within the tracking time-out period withrespect to the signal of each positioning satellite in accordance withthe variations in timing of capture, or it is possible to determinewhether location measurement can be carried out within the trackingtime-out period. Meanwhile, any restrictions as to the possibility ofuse in location measurement depending on the intensity or the S/N ratioor the like of received signals are not set on signals that can becaptured, and the possibility of the above described acquisition isdetermined after acquisition of the data of the sub-frames 1 through 3is tried once. For example, in a case where the signal intensity is notsufficiently high, but the data of the sub-frames 1 through 3 can beacquired in a short time in accordance with the timing of burst noisecontamination or the timing of attenuation of the reception intensitydue to phasing, the acquired data can be effectively used. If locationmeasurement is determined to be difficult through the abovedetermination process, the receiving operation is ended more promptly.If reception is continued, the possibility of successful reception canbe increased.

Accordingly, information from positioning satellites can be acquiredmore efficiently than in conventional cases.

In a case where the precision of the acquired current location does notsatisfy a predetermined condition, the control unit 502 c determineswhether any signal other than the signals related to the data of thesub-frames 1 through 3 used in the location measurement has beencaptured. In a case where the capturing operation has not been ended, orwhere it is determined that a signal other than the signals used in thelocation measurement has been captured, the tracking unit 502 b is madeto continue the acquisition of the data related to the captured signal.In a case where the capturing operation has been ended, and it isdetermined that the data of the sub-frames 1 through 3 acquired from allthe captured signals have been used in the location measurement, the GPSreception processing unit 50 is made to suspend the operation to receiveradio waves from positioning satellites.

That is, in a case where there is a signal captured after the othersignals, or where there is a signal from which the data of thesub-frames 1 through 3 has not been acquired at substantially the sametime as the other signals due to temporary noise, there is a possibilitythat the precision of the location information can be increased, as thepositioning satellite related to the signal is added, and thecoordinates of the positioning satellites are changed. In a case wherethe necessary precision cannot be obtained even though all the data ofthe sub-frames 1 through 3 obtained from captured signals are used, onthe other hand, a change in the coordinates due to movement of thepositioning satellites related to the captured signals cannot beexpected in a short period of time. Also, with only a single locationmeasuring operation, there is a high possibility of unsuccessfulreception due to movement during the operation. Since movement during anoperation is normally not recommended, there is a low possibility that asignal from a new positioning satellite can be captured in a shortperiod of time as the point of reception moves. Therefore, even if alocation measuring operation is repeated, an increase in precision canhardly be expected. Therefore, an operation with a low possibility oflocation measurement with a desired precision or higher is promptlyended, so that the possibility of unnecessary consumption of power andtime can be lowered.

The control unit 502 c also counts the number of times acquisition ofthe data of the sub-frames 1 through 3 has been unsuccessful in thetracking unit 502 b with respect to each captured signal, and suspendsthe acquisition of the data of the sub-frames 1 through 3 with respectto the signals with which the number of unsuccessful acquisition timesis equal to or larger than a predetermined number of times. That is,reception of signals from positioning satellites at low reception levelsis promptly suspended without waste of time, so that locationmeasurement can be carried out only with signals from positioningsatellites from which the data of the sub-frames 1 through 3 areexpected to be acquired. Particularly, signals that are likely to becometemporarily difficult to be received due to noise or phasing, in spiteof the signal intensity to be received, are accurately identified andused or eliminated. In this manner, location measurement can be carriedout quickly without fail.

The control unit 502 c does not cause the capturing unit 502 a tore-search for signals with which acquisition of the data of thesub-frames 1 through 3 has been suspended. As described above, anychange is expected in a short time in a situation where acquisition ofthe sub-frames 1 through 3 is difficult. Therefore, capture and trackingof such signals are not repeated many times, so that unnecessaryconsumption of time and power can be prevented.

In a case where the number of signals captured by the capturing unit 502a is equal to or larger than the predetermined number of signalsnecessary in location measurement, the signal search is ended. In a casewhere the sub-frames 1 through 3 are acquired from three or morepositioning satellites before the predetermined number of signals arecaptured, the control unit 502 c performs control so that locationmeasurement is carried out with the data of the acquired sub-frames 1through 3.

That is, in conventional cases, data is acquired by capturing signalsfrom a sufficiently larger number of positioning satellites than thenumber of necessary satellites in location measurement, so that locationmeasurement is carried out with high precision without fail. In a casewhere signals from the sufficiently larger number of positioningsatellites are not captured, on the other hand, if location measurementis possible, the location measurement is carried out once, and whetherthe current location data related to the location measurement can beused is determined based on the precision of the location measurement.If there is a possibility of successful location in that case, thelocation measurement is carried out. Accordingly, in a case where thecurrent location can be acquired with the necessary precision before thepredetermined number of positioning satellites to be used in locationmeasurement are captured and the data of the sub-frames 1 through 3 areacquired, the reception process can be ended while the current locationis quickly acquired.

In a case where the capture time-out period has passed since thecapturing unit 502 a started searching signals from positioningsatellites, the search is ended. If signals from three or morepositioning satellites necessary for location measurement have beencaptured before the end of the search, the tracking unit 502 b is madeto acquire the data of the sub-frames 1 through 3 from the capturedsignals.

Accordingly, even if the desired number of positioning satellites to beused in conventional location measurement have not been acquired, thepossibility of successful location data acquisition can be increased bycarrying out location measurement, as long as signals from three or morepositioning satellites necessary for location measurement have beenacquired.

The capturing unit 502 a has more than one channel, searches for signalsfrom positioning satellites in parallel through the channels, excludescaptured signals from the signals to be captured, and adjusts the numberof channels to be used in searching for the signals to be captured, inaccordance with the number of the remaining signals to be captured.

Accordingly, electric power is not wasted by unnecessarily turning on achannel even though the number of signals to be searched for hasdecreased. Thus, a signal capturing operation can be efficientlyperformed.

Second Embodiment

Next, an electronic clock according to a second embodiment is described.

FIG. 6 is a block diagram showing the functional structure of anelectronic clock 1 a according to the second embodiment.

This electronic clock 1 a differs from the electronic clock 1 of thefirst embodiment only in that a measuring unit 54 is added. The othercomponents of this embodiment are denoted by the same reference numeralsas those used in the first embodiment, and explanation of them is notprovided herein.

The measuring unit 54 is designed to measure the posture, the state ofmotion, and the like of the electronic clock 1 a. The measuring unit 54includes an acceleration sensor 541 and an orientation sensor 542.

The acceleration sensor 541 is a triaxial sensor for measuring the stateof motion of the electronic clock 1 a, and, for example, measures theaccelerations in two axial directions on the display surface (the planeof rotation of the indexes 61 through 65) of the electronic clock 1 a,and in a direction perpendicular to the display surface. Theacceleration sensor 541 may be a sensor using piezoresistance, forexample.

The orientation sensor 542 is a sensor for measuring the posture(orientation) of the electronic clock 1 a, and measures the orientationof magnetic north. The orientation sensor 542 may be a sensor using amagnetoresistive element (MR element), for example.

A determination program for determining the state of motion of theelectronic clock 1 a is stored in the ROM 42, and the CPU 41 (a movementcalculating unit 411) can determine the state of motion of theelectronic clock 1 a by executing the determination program. Forexample, the direction perpendicular to the ground surface (or thevertical direction) is identified from the gravitational accelerationmeasured by the acceleration sensor 541. Accordingly, the state ofmotion and movement of a user can be determined from a change inacceleration in the vertical direction, a change in acceleration in ahorizontal plane, the direction of movement in the horizontal planemeasured by the orientation sensor 542, and the like. In the case ofmotion that involves movement mainly in a horizontal direction caused byan automobile or a vehicle, the velocity in the horizontal direction andthe movement (a location change) can be calculated (or roughlycalculated) based on a change in the horizontal acceleration. In thecase of motion that involves cyclic changes in acceleration in thevertical direction due to walking or the like, and cyclic changes inacceleration mainly in the display surface of the clock due to swingingof the arms, the number of steps walked by the wearer of the electronicclock 1 a in accordance with the cycles of changes in the accelerator iscounted, and movement can be calculated based on the average length ofstride and the movement direction measured by the orientation sensor542. As an acceleration change pattern in the vertical direction and inthe arm swinging plane related to determination of a walking state, aconventionally-known pattern can be used.

Next, a location measuring operation in the electronic clock 1 a of thisembodiment is described.

In the electronic clock 1 a of this embodiment, movement is measuredbased on the above described measurement carried out by the measuringunit 54 during a location measuring operation. Even if locationmeasurement after the end of a capturing operation is not successful,location measurement is carried out again, as long as movement of thewearer of the electronic clock 1 a is detected or a change in the pointof location measurement is detected.

FIG. 7 is a flowchart showing the control procedures to be carried outby the CPU 41 in a local time acquisition process to be performed by theGPS reception processing unit 50 of the electronic clock 1 a of thisembodiment.

This local time acquisition process differs from the local timeacquisition process of the second modification in the electronic clock 1of the above described first embodiment, in that the procedure in stepS121 is replaced with the procedure in step S121 a, and the proceduresin steps S130 and S132 are added. The same procedures as those of thefirst embodiment are denoted by the same reference numerals as thoseused in the first embodiment, and detailed explanation of them is notprovided herein.

When the process branches into “YES” as a result of the determinationprocedure in step S106 or S109, the control unit 502 c ends theoperation to capture signals from positioning satellites, and transmitsa control signal to the CPU 41 and controls the CPU 41 to calculate themovement after the time based on the measurement data obtained by themeasuring unit 54 (step S121 a).

If the control unit 502 c determines in the determination procedure instep S126 that the number of positioning satellites being tracked issmaller than three (“YES” in step S126), the control unit 502 cdetermines whether the location of the electronic clock 1 a has movedsince the capturing operation was ended in step S121 (step S130).Specifically, the control unit 502 c acquires the relative traveldistance from the location of the end of the capturing operation, therelative travel distance having being measured by the measuring unit 54and calculated by the CPU 41. The control unit 502 c then determineswhether the relative travel distance is equal to or longer than apredetermined distance (reference distance). If the control unit 502 cdetermines that the relative travel distance is equal to or longer thanthe predetermined distance (“YES” in step S130), the process beingperformed by the control unit 502 c returns to step S101, and thecapturing operation is started again. If the control unit 502 cdetermines that the relative travel distance is neither equal to norlonger than the predetermined distance (“NO” in step S130), the processbeing performed by the control unit 502 c moves on to step S133, and thecontrol unit 502 c ends the receiving operation (step S133).

If the process branches into “YES” as a result of the procedure in stepS131, the control unit 502 c determines whether the location of theelectronic clock 1 a has moved after the procedure in step S121 a (stepS132). If the control unit 502 c determines that the location of theelectronic clock 1 a has moved (“YES” in step S132), the process beingperformed by the control unit 502 c moves on to step S101. If thecontrol unit 502 c determines that the location of the electronic clock1 a has not moved (“NO” in step S132), the process being performed bythe control unit 502 c moves on to step S133.

As described above, the electronic clock 1 a of the second embodimentincludes the measuring unit 54 that measures a state of motion, and theCPU 41 (or the movement calculating unit) calculates movement of thelocation based on measurement data obtained by the measuring unit 54,and causes the capturing unit 502 a to suspend the signal search under apredetermined condition. If the distance from the location of thesuspension of the search to the location where acquisition of thecurrent location has failed is equal to or longer than the predeterminedreference distance, the capturing unit 502 a is made to resume thesignal search.

The signal search and the data acquisition period are not simplyprolonged, but the search and the capture are resumed to continue thereceiving operation only when there is a possibility that the point ofreception of radio waves has moved, and the reception environments havechanged, even though reception has failed once. Accordingly, thepossibility of successful acquisition of the current location can beefficiently increased.

It should be noted that the present invention is not limited to theabove described embodiments, and various modifications may be made tothem.

For example, in the above described embodiments, location measurement iscarried out even if signals from only three positioning satellites havebeen received in a local time acquisition process. In a conventionallocation measurement process, however, altitude information is alsorequired, and therefore, current location information may be calculatedand output only if signals from four or more positioning satellites havebeen received.

Also, in the above described embodiments, the data of the sub-frames 1through 3 are received from GPS satellites. In a case where data is tobe received from positioning satellites of a different kind, however,the necessary data range needs to be acquired in accordance with theformat of navigation messages of the positioning satellites. Time-outperiods related to capture and tracking may also be set in accordancewith the format.

Also, in the above described embodiments, the number of times receptionof the data of the sub-frames 1 through 3 required for GPS locationmeasurement has failed is simply counted, and, when the number of timesreception has failed becomes larger than a predetermined number oftimes, the acquisition (tracking) of data from the signal is suspended.However, in a case where the number of times the data of the sub-frames1 through 3 have been received greatly differs between a signal capturedearly and a signal captured later, the tracking may be suspended notwhen the number of times reception has failed becomes larger than thepredetermined number of times, but when the failure frequency or therate of reception failure after the second reception exceeds 50%.

Also, in the above described embodiments, the top of the data of onecycle is not necessarily a sub-frame 1. However, all the tops of datamay be sub-frames 1, and the current location may be calculated only ifthe date is received substantially at the same time within atransmission delay range based on the distances from respectivepositioning satellites.

During a location measurement process (a local time acquisitionprocess), the current location may be calculated using the data ofdifferent frames among positioning satellites. Even in a case where thenumber of times reception of the sub-frames 1 through 3 has failedreaches a predetermined number of times, the data of the sub-frames 1through 3 can be used in location measurement, if all the necessary dataof the sub-frames 1 through 3 have been acquired from different framesbefore the number of times reception has failed reaches thepredetermined number of times. After that, if the current location iscalculated again due to inadequate precision, the data of the sub-frames1 through 3 acquired from the signals of which tracking has beensuspended may not be used.

Also, in the above described embodiments, after the reception period forthe data of the sub-frames 1 through 3 has passed, whether some of thereceived data of the sub-frames 1 through 3 has not been acquired iscollectively determined, and the number of times of reception isincremented by “1” before the next cycle of reception is conducted.However, failure may be detected in real time, and, if failure isdetected more than once in one cycle, the number of times of receptionmay not be incremented after the second reception. Alternatively, whenthe number of times of reception becomes one short of a predeterminednumber of times, failure detection with respect to the signal may beswitched to real-time detection. When unsuccessful acquisition of thedata of the sub-frames 1 through 3 is detected, the tracking of thesignal may be promptly suspended.

Also, in the above described embodiments, an ephemeris is obtained so asto acquire current location information through location measurement.However, in a case where the precision of location measurement may below, a location can be roughly calculated with an almanac. Therefore, ina case where the almanac data of the positioning satellite beingcaptured can be received by some positioning satellite, the almanac datamay be used.

Also, in the above described embodiments, DOP is used as an index ofprecision. However, the index of precision is not necessarily DOP. Forexample, inadequate precision may be detected when the value of acalculated velocity or altitude is outside a range defined by referencevalues that indicate the upper limit value and the lower limit value ofvelocities or altitudes.

Also, in the above described embodiments, a single precision conditionis set. However, the precision condition for positions acquired during acapturing operation or positions acquired without the use of all thecaptured signals may be stricter than the precision condition forpositions acquired after the end of capture or positions acquired withthe use of all the captured signals.

In this case, if the precision condition is determined not to besatisfied after the data of the sub-frames 1 through 3 have beenacquired from three or more satellites through the determinationprocedure in step S112 or S112 b and the process has moved to step S127,the process may not move on to step S131, but may return to theprocedure in step S102.

In the second embodiment, the acceleration sensor 541 and theorientation sensor 542 determine a state of motion and measure a traveldistance. However, some other sensors, such as a horizontal sensor onthe display surface of the electronic clock 1 a, may be used, forexample.

Also, in the second embodiment, whether to allow resumption of search isdetermined based on the relative travel distance at the time of the endof capture. However, in a case where it is difficult to accuratelydetermine the direction of motion and accumulate motion vectorquantities, only the accumulated value of movement (scalar) may besimply set as the reference (reference distance) for determination. Inthis case, the relative travel distance may be short as a result of aseries of movements or a return to the original point. However, if thereis a cause of attenuation of radio waves transmitted from satellites,such as when a shutter or some special-purpose window of a room is leftopen before the user returns to the room, the reception environment canbe improved.

In the above described first through third modifications and the abovedescribed second embodiment, components and procedures are added to thecomponents and the processing procedures of the first embodiment.However, these added components and procedures may be used independentlyof one another or may be combined as appropriate. For example, in thelocal time acquisition process of the first modification, the procedureof step S131 may not be added, and, when the process branches into “NO”as a result of the determination procedure in step S127, the process mayreturn directly to the procedure in step S122.

Other than the above, any appropriate changes can be made to thespecific structures, and the contents and the procedures of theprocesses of the above described embodiments, without departing from thescope of the present invention.

Although embodiments of the present invention have been described sofar, the scope of the present invention is not limited to the abovedescribed embodiments, and includes the inventions disclosed in theclaims and equivalents thereof.

The invention claimed is:
 1. A radio wave receiver that receivessatellite waves, the radio wave receiver comprising: a GPS receptionprocessing unit configured to receive signals from a plurality ofpositioning satellites, acquire data necessary for positioning from thereceived signals, calculate a current location of the radio wavereceiver, save a failure history related to acquisition of the datanecessary for positioning with respect to each of the received signals,determine a reception condition of each of the received signals inaccordance with the failure history, and suspend acquisition of the datanecessary for positioning with respect to a signal having the receptioncondition determined to be at least equal to a predetermined referencelevel, the signal being among the signals from the plurality ofpositioning satellites.
 2. The radio wave receiver according to claim 1,wherein, when the number of signals for which the data necessary forpositioning is to be acquired is smaller than the number of signalsnecessary in calculating the current location after a search for thesignals is ended under a predetermined condition, the GPS receptionprocessing unit ends the reception of the signals from the plurality ofpositioning satellites.
 3. The radio wave receiver according to claim 1,wherein: the GPS reception processing unit receives the signals from theplurality of positioning satellites by searching for and capturingsignals from positioning satellites included in received radio waves,when precision of acquired acquisition target information does notsatisfy a predetermined criterion, the GPS reception processing unitdetermines whether a signal other than signals related to the datanecessary for positioning, the signals related to the data necessary forpositioning having been used in calculating the current location, when asearch for the signals has not been ended, or when the GPS receptionprocessing unit determines that a signal other than the signals used incalculating the current location has been captured, the GPS receptionprocessing unit continues to acquire the data necessary for positioning,and, when the search for the signals has been ended, and the GPSreception processing unit determines that the data necessary forpositioning acquired from all captured signals have been used incalculating the current location, the GPS reception processing unit endsthe acquisition of the data necessary for positioning.
 4. The radio wavereceiver according to claim 1, wherein the GPS reception processing unitcounts the number of times acquisition of the data necessary forpositioning has failed as the failure history with respect to eachsignal, and suspends acquisition of the data necessary for positioningfrom a signal with which the number of times acquisition of the data hasfailed is at least equal to a predetermined number of times.
 5. Theradio wave receiver according to claim 2, wherein the GPS receptionprocessing unit counts the number of times acquisition of the datanecessary for positioning has failed as the failure history with respectto each signal, and suspends acquisition of the data necessary forpositioning from a signal with which the number of times acquisition ofthe data has failed is at least equal to a predetermined number oftimes.
 6. The radio wave receiver according to claim 3, wherein the GPSreception processing unit counts the number of times acquisition of thedata necessary for positioning has failed as the failure history withrespect to each signal, and suspends acquisition of the data necessaryfor positioning from a signal with which the number of times acquisitionof the data has failed is at least equal to a predetermined number oftimes.
 7. The radio wave receiver according to claim 3, wherein the GPSreception processing unit does not re-search for a signal with whichacquisition of the data necessary for positioning has been suspended. 8.The radio wave receiver according to claim 6, wherein the GPS receptionprocessing unit does not re-search for a signal with which acquisitionof the data necessary for positioning has been suspended.
 9. The radiowave receiver according to claim 3, wherein, when a predetermined numberof signals have been captured, the GPS reception processing unit endsthe search for the signals, the predetermined number being at least thesame as the number of signals necessary in calculating the currentlocation, and, when the data has been acquired from at least the samenumber of signals as the number of the signals necessary in calculatingthe current location before the predetermined number of signals arecaptured, the GPS reception processing unit calculates the currentlocation using the data.
 10. The radio wave receiver according to claim6, wherein, when a predetermined number of signals have been captured,the GPS reception processing unit ends the search for the signals, thepredetermined number being at least equal to the number of signalsnecessary in calculating the current location, and, when the data hasbeen acquired from at least the same number of signals as the number ofthe signals necessary in calculating the current location before thepredetermined number of signals are captured, the GPS receptionprocessing unit calculates the current location using the data.
 11. Theradio wave receiver according to claim 3, wherein, when a predeterminedupper limit time has passed since a start of the search for the signals,the GPS reception processing unit ends the search, and, when at leastthe same number of signals as the number of signals necessary incalculating the current location have been captured before the end ofthe search, the GPS reception processing unit acquires the data from thecaptured signals.
 12. The radio wave receiver according to claim 6,wherein, when a predetermined upper limit time has passed since a startof the search for the signals, the GPS reception processing unit endsthe search, and, when at least the same number of signals as the numberof signals necessary in calculating the current location have beencaptured before the end of the search, the GPS reception processing unitacquires the data from the captured signals.
 13. The radio wave receiveraccording to claim 3, wherein the GPS reception processing unit searchesfor signals from a plurality of positioning satellites, excludes eachcaptured signal from capture target signals, and adjusts the number ofthe capture target signals in accordance with the number of remainingcapture target signals.
 14. The radio wave receiver according to claim6, wherein the GPS reception processing unit searches for signals from aplurality of positioning satellites, excludes each captured signal fromcapture target signals, and adjusts the number of the capture targetsignals in accordance with the number of remaining capture targetsignals.
 15. A radio clock comprising: a time measuring unit configuredto measure a current time; a display unit configured to display thecurrent time; and the radio wave receiver according to claim
 1. 16. Aradio wave receiving method for a radio wave receiver including a GPSreception processing unit, the radio wave receiving method comprising: areceiving step of receiving signals from a plurality of positioningsatellites, a current location calculating step of acquiring datanecessary for positioning from the received signals, and calculating acurrent location of the radio wave receiver, a failure history savingstep of saving a failure history related to acquisition of the datanecessary for positioning with respect to each of the received signals,a reception condition determining step of determining a receptioncondition of each of the received signals in accordance with the failurehistory, and a data acquisition suspending step of suspendingacquisition of the data necessary for positioning with respect to asignal having the reception condition determined to be at least equal toa predetermined reference level, the signal being among the signals fromthe plurality of positioning satellites.